The study is designed to evaluate the efficacy & safety of Hu23F2G administered intravenously to patients with acute exacerbations of multiple sclerosis (MS) as compared to placebo and corticosteroid treatment. Hu23F2G is a humanized anti-CD18 monoclonal antibody which has been effective in a non-human primate experimental model of MS. This is a Phase 2 study in which patients will be randomized to treatment for 3 days with placebo, methylprednisoline, or Hu23F2G at 1 or 2 mg/kg. Subjects will be followed for 1 year after treatment.